1. Field of the Invention
This invention relates to a laminated transparency having an edge seal and in particular to an edge seal for a laminated windshield having an electroconductive coating between the outer plies of the windshield.
2a. Technical Considerations
It is well known to coat a major surface of a transparency, e.g. a glass sheet, with a transparent film to enhance the spectral properties of the transparency. For example, the film may be used to reduce the amount of infrared (IR) radiation transmitted through the transparency by reflecting a predetermined bandwidth of radiation. This reduction is especially useful where the transparency is installed in a vehicle, such as an automotive windshield, since the IR radiation is a major cause of heat build-up in a vehicle. The resulting reduction in heat build-up reduces the burden on the vehicle's air conditioning system to maintain a comfortable temperature within the vehicle for its occupants. In addition, if the film is electroconductive, a current may be passed through the film to raise the temperature of the transparency. The elevated temperature of the windshield will melt any ice or snow that accumulates on an exposed surface of the windshield.
In fabricating a laminated transparency such as a windshield with a film positioned between the glass plies, the film can be applied to a flat glass sheet which is subsequently shaped and laminated to a matching glass ply or the film may be applied to a bent glass ply which is then laminated to a matching ply. It has been found that when the film extends to the edge of the laminate, it may degrade due to exposure to the environment. In particular, where the film contains a silver layer, it has observed that sodium chloride from salts will react with the silver forming silver chloride. In addition, high humidity conditions have been found to cause the silver in the silver layer to form aggregates. The results of either or both of these conditions is discoloration of the film, reduced effectiveness of the film as a IR radiation reflecting or heating film, and/or possible delamination of the windshield. The marginal edge of the coated glass ply may be masked, for example with tape prior to coating the glass so that after the coating operation, the tape is removed, leaving an uncoated marginal edge. However, this type of processing requires precise positioning of the tape prior to coating and removal of the tape after coating as well as introducing the possibility of contaminating the film during a coating operation.
It would be advantageous to provide a material to seal the periphery of a coated laminate to prevent degradation of its film coating.
2b. Patents of Interest
U.S. Pat. Nos. 3,752,348 to Dickason et al.; 4,543,466, 4,668,270, and 4,743,741 to Ramus; 4,654,067 and 4,725,710 to Ramus et al.; 4,718,932 to Pharms; 4,744,844 to Hurst; 4,778,732 to Hasegawa et al. and 4,786,784 to Nikodem et al. teach a heatable windshield with opposing bus bars interconnected by an electroconductive coating on an interior glass surface of the windshield.
U.S. Pat. No. 3,790,752 to Boaz et al. teaches a heatable laminated windshield wherein the electrical connection to the electrically conductive coating of the windshield is made within a notch in the windshield interlayer material.
U.S. Pat. Nos. 3,794,809 to Beck et al.; 4,368,945 Fujimori et al. and 4,782,216 to Woodward teach a vehicle windshield with an electroconductive coating disposed between first and second laminating interlayers. In Beck et al., the coating is spaced inwardly from the edge of the glass plies of the windshield a sufficient amount to seal the coating within the interlayer.
U.S. Pat. No. 4,278,875 to Bain teaches an electrically heated window with a tin oxide coating extending to the edge of the window. The edge of the window is seal by an elastomeric sealant and a peripheral channel.
U.S. Pat. No. 4,284,677 to Herliczek teaches an electrically heated laminated aircraft glazing with an electroconductive coating. A layer of polyisobutylene resin is provided between the interlayer material and selected glass areas to prevent delamination and cold chipping of the glazing with subsequent moisture ingress and bus bar failure.